Adaptive controls of engine disconnect clutch

Abstract

A hybrid vehicle includes an engine, an electric machine, and a clutch configured to selectively couple the engine to the electric machine. A controller is programmed to command a torque to the electric machine based on a clutch model that includes a learned time constant previously selected using a family of candidate time constants based on a comparison of the family to measured pressure data of a previous engagement of the clutch.

What is claimed is: 
     
       1. A hybrid vehicle comprising:
 an engine; 
 an electric machine; 
 a clutch configured to selectively couple the engine to the electric machine; and 
 a controller programmed to, responsive to an engine-start request, command a torque to the electric machine based on a clutch model that includes a learned time constant previously selected from a family of candidate time constants, each associated with a candidate clutch model, based on a comparison of the candidate clutch model to measured pressure data of a previous engagement of the clutch. 
 
     
     
       2. The hybrid vehicle of  claim 1 , wherein the candidate clutch model associated with the previously selected learned time constant has a slope nearer to a slope of the measured pressure data than non-selected ones of the candidate clutch models. 
     
     
       3. The hybrid vehicle of  claim 1 , wherein amplitudes of the candidate clutch models do not exceed a maximum value of the measured pressure data by a predetermined amount. 
     
     
       4. The hybrid vehicle of  claim 3 , wherein the predetermined amount is a predetermined percentage. 
     
     
       5. A hybrid vehicle comprising:
 an engine; 
 an electric machine; 
 a clutch configured to selectively couple the engine to the electric machine; 
 a pressure sensor associated with the clutch and configured to output the measured pressure data to the controller; and 
 a controller programmed to, responsive to an engine-start request, command a torque to the electric machine based on a clutch model that includes a learned time constant previously selected from a family of candidate time constants, each associated with a candidate clutch model, based on a comparison of the candidate clutch model to measured pressure data of a previous engagement of the clutch. 
 
     
     
       6. The hybrid vehicle of  claim 1 , wherein the controller is further programmed to discard the learned time constant responsive to a fluid temperature associated with the clutch being outside a threshold. 
     
     
       7. The hybrid vehicle of  claim 1 , wherein the family of candidate time constants includes at least two candidate time constants. 
     
     
       8. The hybrid vehicle of  claim 1 , wherein the comparison includes comparing slopes of the candidate clutch models to a slope of the measured pressure data. 
     
     
       9. The hybrid vehicle of  claim 8 , wherein the controller is further programmed to:
 select the one of the candidate clutch models having the slope nearest to the slope of the measured pressure data; and 
 select the candidate time constant of the one of the candidate clutch models as the learned time constant. 
 
     
     
       10. A hybrid vehicle comprising:
 an engine; 
 an electric machine; 
 a clutch configured to selectively couple the engine to the electric machine; and 
 a controller programmed to command a torque to the electric machine based on a clutch model that includes a learned time constant previously selected using a family of candidate time constants based on a comparison of the family to measured pressure data of a previous engagement of the clutch. 
 
     
     
       11. The hybrid vehicle of  claim 10 , wherein the comparison includes comparing the candidate time constants to a slope of the measured pressure data. 
     
     
       12. The hybrid vehicle of  claim 10 , wherein the controller is further programmed to select the one of the candidate time constants nearest to the slope of the measured pressure data. 
     
     
       13. The hybrid vehicle of  claim 10 , wherein the controller is further programmed to select a value for the learned time constant by interpolation between one or more of the candidate time constants nearest to the slope of the measured pressure data. 
     
     
       14. The hybrid vehicle of  claim 10  further comprising a pressure sensor associated with the clutch and configured to output the measured pressure data to the controller, wherein the pressure sensor is in fluid communication with the clutch. 
     
     
       15. The hybrid vehicle of  claim 10 , wherein the controller is further programmed to discard the learned time constant responsive to a fluid temperature associated with the clutch being outside a threshold. 
     
     
       16. The hybrid vehicle of  claim 10 , wherein the controller is further programmed to discard the learned time constant responsive to a line pressure associated with the clutch being outside a threshold. 
     
     
       17. The hybrid vehicle of  claim 5 , wherein the candidate clutch model associated with the previously selected learned time constant has a slope nearer to a slope of the measured pressure data than non-selected ones of the candidate clutch models. 
     
     
       18. The hybrid vehicle of  claim 5 , wherein amplitudes of the candidate clutch models do not exceed a maximum value of the measured pressure data by a predetermined amount. 
     
     
       19. The hybrid vehicle of  claim 18 , wherein the predetermined amount is a predetermined percentage. 
     
     
       20. The hybrid vehicle of  claim 5 , wherein the controller is further programmed to:
 select the one of the candidate clutch models having the slope nearest to the slope of the measured pressure data; and 
 select the candidate time constant of the one of the candidate clutch models as the learned time constant.